A partially or totally drained automotive battery is often unable to supply enough power to start an automobile. Further, certain charged batteries may not be able to supply the necessary cranking power to start an automobile under adverse environmental conditions. For example, at very cold temperatures, the potential across a charged battery can drop drastically, thus lessening its overall power output. For example, in cold weather the voltage of a normal 6cell, 12 volt automotive battery will typically drop to 5 to 7 volts. This lower voltage may not be able to supply a starting motor with sufficient cranking power. As a result, the engine may turn over at a lower RPM, or not at all.
The problem caused by the high current demand of the starting motor has prompted efforts to augment the power of an automobile battery during starting. In one known approach, an auxiliary battery is used to supply extra power at starting, but is otherwise isolated during main battery drain. Such a system is shown in European Patent Publication No. 398,691 issued to Witehira, in which the auxiliary battery is coupled in parallel to the main battery in response to an indication that the vehicle is being started. A disadvantage of this approach is that the auxiliary battery switches-in at starting whether or not a power boost is needed.
To alleviate this problem, some systems provide a manual switch to actuate the coupling of the auxiliary battery to the main battery. Such an approach is shown in U.S. Pat. No. 5,002,840 issued to Klebenow, et al. Under this approach, an operator is able to switch-in the extra battery whenever he desires. However, this approach also has significant disadvantages. For example, the manual switch is often located in an inconvenient place, such as under the hood, to avoid excessive wiring. Further, an operator does not always know when extra power is needed.
A further disadvantage of many of the present switch-in systems is that an open circuit between the main battery and the load is created during the switch-in. While the circuit remains open fur a relatively brief time, the voltage drop caused thereby, followed by the voltage surge that occurs when the switch is complete, may cause considerable wear on the electrical components of the power system.
In view of the forgoing, it would be desirable to provide a power control system which is capable of augmenting the power of a primary automotive battery at starting when the primary automotive battery alone is unable to supply sufficient power to start the engine.
It would further be desirable to provide a power control system which has a circuit capable of sensing when the primary automotive battery is unable to supply sufficient cranking power, and when such is the case, to automatically "switch-in" an auxiliary battery.